Design Of Series-Connection Distributed Data Acquisition System Based On EtherCAT Bus

Aiming at the problems of the large amount of data, geographically fragmented acquisition positions, high real-time performance demanding and a variety of data types in the process of data acquisition, we build a series-connection data acquisition system based on EtherCAT bus. EtherCAT is one of the industrial Ethernet protocols with highest real-time performance and reliability. It uses the improved Ethernet protocol architecture and hardware to complete protocol function to guarantee real-time performance and reliability of the communications. The system containing one single master station and multiple slave stations is developed based on the EtherCAT bus. The master station is a PC with NIC. Slave station uses the special control chip to complete communication tasks. In this system every sensors with 1-5V voltage signal output can be connected to the slave station to acquire a variety of physical quantities. Each slave station connected to the system has only one sensor, and the sensor is arranged in the acquisition position together with the flexibility to increase or decrease the number of slaves according to the number of acquisition positions, so the data acquisition system is very suitable for data acquisition and monitoring applications which have large number of geographically fragmented acquisition positions.This paper firstly introduces the research status and the trend of the development of data acquisition systems, and the conclusion is that distributed data acquisition system is main developing tendency. Comparing analysis of several popular industrial ethernet protocols, the results show that the parameters of EtherCAT are outstanding. Then, the overall structure and operating principles of the system are introduced in detail. Secondly, the paper explains the principle of EtherCAT protocol separately from the points of view of the overall structure, the physical layer, data link layer and application layer. Then, the paper states the design process of system master station software, including the software functional requirements analysis, multi-thread technology and multi-media timer programming methods. Thirdly, the paper analyzes the characteristics of the system slave station circuit. The slave circuit is divided into four modules EtherCAT network communication module, analog signal processing module, microprocessor control module and power management module. The key parts of the circuit schematics of each module are given. Next this paper introduces the PCB design of the circuit board. Finally, we build a wave height data aquisition platform based on the system, test and analyze the various parameters of the system by capturing the height of wave in our lab. The experimental results indicate that the system has high reliability linearity and real-time performance. The highest data acquisition frequency is up to 1kHz, and the response time is only about 250us. The designed data acquisition system can reach the original expectation well.